Definition - What does Gray Rot mean?
Gray rot is synonymous with the names Botrytis cinerea (Boytritis for short) and noble rot. Its name comes from the color it gives infected grapes. The disease occurs in special conditions within a wet and humid climate, and the grapes take on the appearance of gray fur.
For some winemakers, it can be desired, especially for white wine grapes, as it concentrates the sugars of the fruit by dehydration and maintains natural acidity.
WineFrog explains Gray Rot
Gray rot is also known as Botrytis cinerea, or noble rot. The phenomenon of gray rot only occurs in ideal conditions of a wet and humid climate. These conditions are so rare, that there are only a few pockets in the world where it occurs. Typically, these areas are found near a large body of water with and influence of warmer winds.
The most famous regions where noble rot forms and where botrytized wines are found are Tokaj, Hungary, the Rheingau region of Germany and Sauternes and Barsac of Bordeaux. Parts of wine regions in Ontario and Northern Italy also enjoy the effect of gray rot.
The rot is favorable, though mostly only for white wine grapes, as it reduces the water content of the grape while maintaining natural acidity and concentrating its sugars. The result of wine made with these grapes are sought after worldwide for their sweet honey aromas and flavors.